Seamless pipe mills have been employed for a good many years for producing seamless steel tubular products. These continuous rolling mills are generally constructed having a plurality (usually nine) of tandem individually powered stands of two-high grooved rolls. The rolls in the consecutive stands have their axes at 90 degrees to each other. The seamless pipe mill requires an internal mandrel against which the work piece is rolled to reduce wall thickness. This cylindrical mandrel extends entirely through a pierced billet (also known as a shell) and passes through the mill with the work piece. In the first two roll stands, the diameter of the pierced shell is reduced so that the inner surface is in substantial contact with the mandrel bar. Successive stands of rolls each make reductions in the wall of the shell with reductions getting less with each successive roll. By the ninth stand, there is very little reduction, the major purpose being to plane the tube surface. The shape of the tube which has been oval in the proceeding stands is changed to circular by the ninth stand. The rounding up operation effected by this stand frees the inner surface of the tube from the mandrel bar to facilitate the withdrawal of the mandrel therefrom.
In the operation of the mill, after a billet has been pierced by a conventional Mannesmann piercing mill, a lubricated mandrel, considerably longer than the pierced shell, is inserted and both pass through the rolling mill. The tube and mandrel are then kicked out of the pass line to a stripper which mechanically removes the mandrel.
The lubricant which is applied to the mandrel bar is employed for the purpose of alleviating any tendency of the tube to stick to the mandrel. These "stickers" are undesirable insofar as they require additional time to strip the tube from the mandrel and may, if sticking becomes a serious enough problem, result in the necessity to destroy the tube in order to remove the mandrel. It should be obvious that such counterproductive operations cannot be long tolerated. Heretofore, the lubricant used for coating the mandrel bar was black oil. The use of black oil was successful and has been recognized as the lubricant for mandrel bars. Black oil, however, is a hydrocarbon and produces thick deleterious smoke when burned (as happens when the lubricant is applied to the mandrel and the latter is inserted into the hot shell). The level of smoke in the mills became dangerous to the health and safety of the employees of the mill even though it worked very well in keeping mills loads constant and alleviating stickers.
The Environmental Protection Agency (EPA) and the Occupational Safety and Health Act (OSHA) both have direct bearing upon the above-noted situation. Specifically, the EPA objected to the use of black oil, or any hydrocarbon lubricant, in the mill for the obvious reason that the smoke produced polluted the surrounding atmosphere. The promulgators of OSHA expressed the same type of concern for the workers forced to breath the smoke and work in the reduced visibility environment resultant from such use. The only solution available was to find a substitute for the black oil which was not a smoking hydrocarbon and which did not present other disadvantages or safety problems.
An initial testing period conducted by applicants resulted in a finding that a graphite and water dispersion on the order of 15 percent graphite is ineffectual. Sticking and pinning occurs shortly after testing of several graphite lubricants commenced. Applicants then, after conducting an in depth research study on the problem, decided that an extremely high non-colloidal graphite dispersion in water might be effective. Colloidal graphite cannot be used because it is inherently too fine and does not fill the irregularities in the mandrel bars sufficiently to prevent sticking. The remaining problem concerns how to apply a high graphite dispersion to a mandrel bar as it enters the shell and is run through the rolls of the mill at speeds approximating 600 feet per minute. The specific solution to this problem is the subject of the present application.